TENS of thousands of motorists using one of the country's busiest motorways face major disruption with the closure of two lanes of traffic to repair a bump in the road.

One of the key arteries into Dublin will be impacted by a series of road improvements planned by Westmeath County Council. Motorists driving east on the N4 are facing two days of traffic chaos on September 15 and September 16.

The council plan to close both eastbound lanes - only opened to the public in May of last year - between Mullingar and Kinnegad.

The planned two-day closure has provoked angry reaction from local businessmen and farmers.

Up to 45 minutes will be added to the average travelling time for those journeying from the west of Ireland to the capital.

All eastbound traffic, including Bus Eireann vehicles, will have to divert from Mullingar, via the N52 to Tyrrellspass, and then on to Kinnegad, by way of the N6.

Westmeath Council maintains the closure is necessitated by "a small section of the road not being completed to the contract specification" resulting in irregular surface levels.

"The diversion is an additional 23km. I estimate it will add between 15 and 20 minutes to journeys in normal traffic," said Michael Connolly, a senior engineer with Westmeath County Council.

"If there are backlogs at peak hours it could be up to 45 minutes delay," he added.

A spokesman for Thomas Flynn & Sons, an agricultural business along the route, said the closure was "madness" as it comes at the height of harvest season.

"Thousands of farmers drop grain here during September, and we're busy with other operations as well. Could they not have found a one-lane solution to this?"

However, a council spokesperson said a one-lane option was not possible in the circumstances due to "traffic safety restrictions."

The relevant section of the N4 road was resurfaced 15 months ago as part of the €14m road improvement plan.

A spokesman for the National Roads Authority told the Irish Independent that the cost of the repair work is being borne by the contractor.